1. Technical Field
The present invention relates generally to methods for high throughput screening of lubricating oil compositions.
2. Description of the Related Art
The use of a combinatorial approach for materials synthesis is a relatively new area of research aimed at using rapid synthesis and screening methods to build libraries of polymeric, inorganic or solid state materials. For example, advances in reactor technology have empowered chemists and engineers to rapidly produce large libraries of discrete organic molecules in the pursuit of new drug discovery, which have led to the development of a growing branch of research called combinatorial chemistry. Combinatorial chemistry generally refers to methods and materials for creating collections of diverse materials or compounds—commonly known as libraries—and to techniques and instruments for evaluating or screening libraries for desirable properties.
Presently, research in the lubricant industry involves individually forming candidate lubricating oil compositions and then performing a macro-scale analysis of the candidate compositions by employing a large amount of the candidate to be tested. Additionally, the methods employed for testing each candidate composition require manual operation. This, in turn, significantly reduces the number of compositions that can be tested and identified as leading compositions.
Drawbacks associated with conventional screening procedures can be seen as follows. For example, governmental and automotive industry pressure towards reducing the phosphorous and sulfur content of lubricating oil compositions used as, for example, passenger car and heavy duty diesel engine oils, is leading to new research to identify oil compositions which can satisfy certain tests such as, for example, oxidation, wear and compatibility tests, while containing low levels of phosphorous and sulfur. In this context, United States Military Standards MIL-L-46152E and the ILSAC Standards defined by the Japanese and United States Automobile Industry Association at present require the phosphorous content of engine oils to be at or below 0.10 wt. % with future phosphorous content being proposed to even lower levels, e.g., 0.08 wt. % by June, 2004 and below 0.05 wt. % by January, 2006. Also, at present, there is no industry standard requirement for sulfur content in engine oils, but it has been proposed that the sulfur content be below 0.3 wt. % to meet June, 2007 requirements for emissions. Thus, it would be desirable to decrease the amount of phosphorous and sulfur in lubricating oils still further, thereby meeting future industry standard proposed phosphorous and sulfur contents in the engine oil while still retaining the oxidation or corrosion inhibiting properties and antiwear properties of the higher phosphorous and sulfur content engine oils. In order to accomplish this, a large number of proposed lubricating oil compositions must be tested to determine which compositions may be useful.
Additionally, similar changes in specifications and changing customer needs also drive reformulation efforts in other lubricant applications such as, for example, transmission fluids, hydraulic fluids, gear oils, marine cylinder oils, compressor oils, refrigeration lubricants and the like.
However, as stated above, present research in the lubricant industry does not allow for reformulation to occur in an expeditious manner. As such, there exists a need in the art for a more efficient, economical and systematic approach for the preparation of lubricating oil compositions and screening of such compositions. For example, many lubricating oil compositions have deposit forming tendencies. Generally, deposit formation on hot and cold components of the engine includes the formation of gummy layers (of brown to black color) or harder deposits which are primarily carbon based deposits. These deposits impair the function of individual components such as, for example, free movement of the piston rings, constriction of air-conveying components of the turbocharger, etc. Consequently, serious engine damage or power loss is suffered in addition to an increase in exhaust-gas emissions. Furthermore, a spongy deposit layer forms preferentially on the horizontal surfaces of the oil space, and in the extreme case may also clog oil filters and oil ducts of the engine, potentially leading to engine damage.
Deposit formation also occurs when, for example, internal combustion engines of automobiles or trucks are subjected to a demanding environment during use. The environment results in the oil suffering oxidation which is catalyzed by the presence of impurity species in the oil such as, for example, iron compounds, and is also promoted by the elevated temperatures experienced by the oil during use. The catalyzed oxidation of the oil contributes to the formation of corrosive oxidation products and sludge in the oil but can also cause the viscosity of the oil to increase or even solidify.
Accordingly, it would be desirable to rapidly screen a plurality of sample candidate lubricating oil compositions for deposit formation tendencies utilizing small amounts of each sample. In this manner, a high throughput preparation and screening of a vast number of diverse compositions can be achieved to identify which additives and/or compositions have reduced deposit formation tendencies.